If the original BP still has the "SSSS" designation on it you are not supposed to be able to board the plane unless the BP is noted by the TSA. With the readers it beeps special and requires the agent to swipe their badge to indicate that they checked it out. Without the reader they're still supposed to check it.

You might slide by but it also may just turn out to be a pain after the fact.

Plus, depending on the airport, the SSSS really adds 2-8 minutes to the process. Heck, at the LGA Marine Air Terminal it takes about 30 seconds extra. It is clearly a waste of time that does nothing to actually increase the security of air travel, but at the same time, it really isn't such a big deal that it is worth getting worked up about.